Lightning strikes on aircraft are known to occur. Conventionally, the fuselage and wings of airplanes were made of lightweight metal such as aluminum. Electrical current from lightning generally travels along the outer skin of such airplanes, causing little damage. Conventional airplane metal exteriors exhibit isotropic conductivity, and can carry even large currents in a well-defined and well-understood manner. Testing for lightning survivability is relatively straightforward. The current density over the exterior surface of an airplane in a lightning strike is usually highly uniform. Hence, a local current measured at one spot may reasonably be considered representative of what is occurring over the entire airplane.
Many modern airplanes are built of composite materials rather than metal. Composites may be lighter and more flexible than metal, with higher elasticity and the ability to embed electronics, such as antennas, into the composite material. Composite airframes are often fabricated in layers. In particular, they may include conductive layers, such as those constructed of carbon fiber, separated by dielectric layers, such as those constructed of various resins. The conductive layers generally exhibit non-isotropic conductivity, such as along the direction of the constituent fibers. Consequently, current density over a composite airframe in a lightning strike is usually non-homogenous, and may be quite complex. This greatly complicates lightning strike research and testing, as it may be difficult to predict or measure current density over the large surface areas.
The Background section of this document is provided to place aspects of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.